Direct Current Networks Research Articles

Enhanced Coil Design for Inductive Power-Transfer-Based Power Supply in Medium-Voltage Direct Current Sensors

This paper presents an integrated coil design method for inductive power-transfer (IPT) systems. Because a medium-voltage direct current (MVDC) distribution network transmits power at relatively high voltages (typically in the tens of kV), accurate fault diagnosis using high-performance sensors is crucial to improve the safety of MVDC distribution networks. With the increasing power consumption of high-performance sensors, conventional power supplies using optical converters with 5 W-class output characteristics face limitations in achieving the rated output power. Therefore, this paper proposes a safe and reliable power supply method using the principle of IPT to securely maintain the insulation distance between the distribution network and the current sensor-supply line. A 100 W prototype IPT system is investigated, and its feasibility is validated by comparing its performance with conventional optical converters.

Development of on-board power systems and the concept of a more electric aircraft

The article reviews the main stages of development of aircraft power systems. The basic features of the power node for the Mi-24 combat helicopter, a multi-tasking aircraft, are presented F-22 and the Boeing B-787 passenger airplane. The results of the analysis of methods for managing the distribution of electricity on both conventional aircraft and the most modern aircraft structures (A-380, B-787) are presented. The basic structures of the aircraft's on-board power network are presented, divided into three periods: the period until the 1960s (with the dominance of the direct current network with a voltage of 28.5 V), the period until 2000 (with the dominance of the three-phase alternating current network with a voltage of 3 x 115 V / 200 V, 400 Hz) and the most recent period, after 2000 (dominated by a 270 V direct current network, obtained by converting the voltage from a three-phase alternating current generator 3x 115 V / 200 V, 400 Hz using a transformer-rectifier block). The concept of a more electric aircraft was presented as the main direction of current construction works for MEA concept (More Electric Aircraft).

Enhancing DC distribution network efficiency through optimal power coordination in lithium-ion batteries: A sparse nonlinear optimization approach

This work deals with the problem regarding the optimal operation of lithium-ion batteries to improve the economic, technical, and environmental indices of standalone and grid-connected direct current (DC) distribution networks.To this effect, a general nonlinear programming model has been developed, which considers three objective functions: (i) the daily energy purchasing costs at the terminals of the substation, considering the maintenance costs of renewable generation (photovoltaic) and energy storage technologies (batteries); (ii) the daily energy losses associated with energy transport; and (iii) the CO2 emissions per day of operation, associated with conventional generators. This is done by integrating all the operations and technical constraints of the DC network and the devices it comprises. The sparse nonlinear optimization (SNOPT) solution method is employed, comparing its results against those of three recently reported metaheuristic optimization methodologies: the continuous genetic algorithm and the parallel versions of the particle swarm optimizer and the vortex search algorithm. The performance of the proposed methodology is validated on standalone and grid-connected networks, considering the technical and economic conditions of two regions of Colombia (rural and urban territories) and evaluating its effectiveness in terms of solution quality, standard deviation, and processing times. The results show that the SNOPT tool of the General Algebraic Modeling System (GAMS) achieves the global optimum in all test scenarios, exhibiting a standard deviation of zero and requiring less than three seconds on average to generate a solution for an entire day of operation.

Faulty feeder detection based on the fluctuation characteristics of inflection point dense area for DC distribution network

A flexible direct current (DC) distribution network based on modular multilevel converter (MMC), with the advantages of no phase change failure and fewer current conversion links. It has gradually become the development trend of future medium voltage distribution networks. However, when a single-pole ground fault occurs in the feeder, the converter's low inertia and weak damping characteristics lead to a fast-rising fault current with a high peak value, which is harmful to the system. In this paper, for the difficulty of accurately selecting the faulty feeder when a single-pole ground fault occurs in a radial DC distribution network, a detection method based on the zero-mode current within the inflection point dense area (IPDA) for the fluctuation characteristics of concave and convexity (FCCC) is proposed. Firstly, the zero-mode current of each feeder is processed using a low-pass filter to select the eigen-components; Then, taking second order derivatives of the eigen-components, and the IPDA is established, to find a period in micro measurement to achieve accurate direction correspondence with opposite directions; Again, the data within IPDA is normalized; the criterion is constructed by determining each feeder's FCCC. Finally, the simulation model is built by Power Systems Computer Aided Design to verify that the method can identify the faulty feeder in various situations. Compared with existing methods, the fault detection method proposed in this paper has good stability and can withstand large grounding resistances.

FEM-Circuit co-simulation of superconducting synchronous wind generators connected to a DC network using the homogenized J–A formulation of the Maxwell equations

High-temperature superconductors (HTS) are greatly appealing for the development of high efficient, and high energy density power devices. They are particularly relevant for applications requiring light and compact machines such as wind power generation. In this context, to ensure the proper design of the superconducting machines and their reliable operation in power systems, it is then important to develop models that can accurately include their physics but also can describe properly their interaction with the system. To achieve such a goal, one approach is the co-simulation. This numerical technique can bring fine geometrical and physical details of the machines through a finite element model (FEM) meanwhile dealing with the operation of the whole system that incorporates the machine and a subset of the power grid represented by an external electrical circuit. The goal of the present work is to put to use this numerical technique when superconducting components are involved. Here, a case study is proposed involving a 15 MW hybrid superconducting synchronous generator (HTS rotor and conventional stator) coupled to a direct current network via a rectifier and its associated filter. The case study related to wind power application allows grasping the technical issues when employing co-simulation dealing with HTS machines. The FEM of the generator is done in the commercial software COMSOL Multiphysics, which interacts with the circuit simulator Simulink through the built-in Functional Mock-up Unit. For the present study, a new version of the latest J–A formulation combined with homogenization technique is introduced allowing an even faster computation time compared to the T–A formulation. Distributed variables and global variables such as current density, magnetic flux density, and local losses for the former and voltage, current, electromagnetic torque, and power quality for the latter are estimated and compared for both formulations. The idea is to find the best-suited combination FEM-circuit under criteria of computational speed, accuracy, and numerical stability. Thus, it is shown that all formulations generate an error of less than 5% on the machine parameters and that the J–A formulation with first order elements stands out with a significant 4-fold reduction in computational costs.

АНАЛІЗ РЕЗУЛЬТАТІВ ЕКСПЕРИМЕНТАЛЬНИХ ДОСЛІДЖЕНЬ НЕОДНОРІДНОСТІ МЕРЕЖІ ПОСТІЙНОГО СТРУМУ

The modes of breakage of one line of network sections with parallel lines in electrical distribution networks of power supply to consumers of direct current electric transport have been studied. An analysis of the experimental data was carried out, the results of which indicate the presence of a dependence of the value of the variable component in the rectified current on the distance to the damaged area. Mathematical modeling of the breakage mode of one of the line sections in the network with a serial connection of three sections, each of which has parallel lines, has been carried out. The obtained results of mathematical modeling of the modes of operation of a direct current network with heterogeneity of different sections also indicate the possibility of using the sixth harmonic of the current to determine the occurrence of heterogeneity and the section with this heterogeneity. To reduce the influence of load changes when determining an inhomogeneous section, it is proposed to control the input impedance of the network at a frequency of 300 Hz. It has been established that in these regimes the resistance angle changes the most. A method for determining the occurrence of local damage to a direct current line and the distance to this damage location is proposed, which is based on moni-toring the value of the line current and the input resistance of the line at a frequency of 300 Hz. References 7, Figures 4, Tables 2.

Centralized event-based protection based on communication infrastructure of medium voltage direct current network

Direct current (DC) distribution systems play a crucial role in integrating various DC systems, renewable energy sources, and power loads. Single-ended protection methods are inadequate for ensuring high-speed selective protection due to the lack of boundary elements, while current differential protection methods can be affected by line-distributed capacitance currents. Therefore, an event-based protection scheme is proposed that uses communication infrastructure and the first derivative of the transient fault current to provide a selective protection system for Medium Voltage Direct Current (MVDC) networks. The scheme utilizes Intelligent Electronic Devices (IEDs) to transmit events to the Intelligent Protection Center (IPC) via a communication network, which compares them to identify the faulty section. The proposed protection scheme is effective in detecting and isolating faults, even under challenging network conditions, as demonstrated by simulation results on a two-terminal topology MVDC distribution network using the PSCAD/EMTDC platform.

DEVICE FOR CONTROLLING PARAMETERS OF ACCUMULATOR BATTERIES AND THE CORRESPONDING DIRECT CURRENT NETWORK

Mobile devices for information, control and telemetry systems are powered by mobile generators through AC to DC converters, by batteries or, if possible, directly by solar panels. Solar panels typically work in a system that involves the usage of batteries to keep the systems running when the solar panels are not working or not providing enough power. The batteries can be recharged from the panels themselves if the solar panels have sufficient power or from an external direct current source. Also, for some mobile devices, power systems are used only with batteries, which are recharged from generators or, if possible, from standard electrical networks. All these options of power supply systems for mobile devices require operational control of battery parameters and corresponding direct current networks. The paper proposes a device for monitoring the following parameters: voltage of the direct current network from which the mobile device is powered or the batteries are charged; battery charge current control; control of insulation resistance of direct current circuits; control of the voltage of chargers; monitoring the status of chargers; protection of batteries from deep discharge; control of the state of switching nodes. The device is implemented as a two-processor system based on STM32F103 microcontrollers. A non-contact sensor of the LEM LA 100-P type is used to measure the direct current, which generates an analog signal proportional to the value of the direct current. This signal is passed to a 16- bit analog-to-digital converter. Given that these microcontrollers have integrated 12-bit analog-to- digital converters, an external 16-bit analog-to-digital converter of the ADS1115 type is used to ensure the necessary accuracy of direct current and voltage measurement, which transmits information to the basic processor via the I2C interface. The basic processor implements the main operating modes of the device, and the local processor provides information exchange with the general mobile power supply system through the RS-485 interface. The device is equipped with an indication system based on an LCD indicator of the VS1602A type and functionally programmable single LED indicators, a local keyboard for selecting control modes, a USB port for connecting additional modules and a SWD port for programming the Flash memory of microcontrollers and debugging programs in real time. During operation, parameters of non-standard events are stored in the device's non-volatile memory. The software of the basic and local processors has been developed, which ensures the functioning of the device in basic modes and performs periodic self-diagnosis of the device. The obtained results can be used in scientific research and in the design of real automated power systems for mobile information systems. Keywords: power systems of mobile information systems, batteries, battery charging, microcontroller, LCD indicator, I2C interface, USB interface, RS-485 interface, SWD interface.

Enhancing PV distributed generator planning in medium‐voltage DC distribution networks: A multi‐design techno‐economic analysis with load demand response

AbstractDistributed generators have grown in significance for the technical and financial operation of electric power systems in recent years. The integration of these generators into the electrical distribution network (EDN) has experienced rapid growth, primarily driven by advancements in renewable energy sources (RESs), particularly photovoltaic distributed generators (PVDGs). With the increasing implementation of solar energy as a RES, designing the optimal integration of PVDGs into medium voltage direct current (MVDC) networks is crucial to comprehensively analyzing technical and economic factors. To address this issue, a new multiple objective function (MOF) is proposed, which combines various techno‐economic parameters such as total active power loss (APL), voltage deviation (VD), and the investment cost of PVDGs (ICPVDG) installed in the test system. The objective is to minimize the MOF simultaneously to achieve the optimal incorporation of PVDGs. This study aims to solve the allocation problems related to the location and size of PVDG units in the modified MVDC test systems IEEE 27 and 33‐bus. Simulation results demonstrate the superior accuracy and effectiveness of the equilibrium optimization algorithm (EOA) in achieving the minimum MOF. The utilization of multiple PVDG units reduces overall active power losses and improves voltage profiles across all buses.

Protection Scheme based on Artificial Neural Network for Fault Detection and Classification in Low Voltage PV-Based DC Microgrid

With the expansion of the DC distribution market, protection, and operational concerns for Direct Current (DC) Microgrids have increased. Different systems have been investigated for detecting, finding, and isolating defects utilising a variety of protective mechanisms. It might be difficult to locate high-resistance faults and shorted DC faults on low-voltage DC (LVDC) microgrids. Therefore, in this study, a Field Transform Technique like Short-Time Fourier Transform (STFT) is proposed for detecting the Fault Current (FC). This method detects the faults Pole-ground (PG), pole-pole (PP), and Arc fault are the major fault types in the DC network with PG fault as the most common and less severe. One of the difficulties the DC system faces in the incidence of a malfunction is the protection of essential converters. During this fault, the diodes, being the most vulnerable component of the system, may encounter a substantial surge in current, which can potentially cause damage if the current surpasses double their specified capacity for withstanding. After the Fault detection (FD), a Taguchi-based ANN is presented to classify the detected faults. This method effectively classifies PV-based faults. Then, to safeguard the FC, the Improved Self-Adaptive Solid State Circuit Breaker (I-SSCB) is introduced. It safeguards the FC in the low-voltage PV-based DC microgrid (DCMG) and restricts FC in the DCMG. The suggested approach is evaluated using the Matlab software and the proposed method produces 400A current and 100 KW power during the PV temperature of 25°C. The output current of the ANN is then 1A for a duration of 0.3 to 0.4 seconds. The fault voltage and FC produced in this proposed work are 1900V and 1950A. Therefore, the proposed work's current and voltage values are 21 KV and 0.35 I. Therefore, the proposed method produces more power and limits the FC in the LV-DCMG. In future studies, the improved or modified neural network or machine learning (ML)-based techniques can be utilized which may improve the protection scheme of the work.

Linearized power flow calculation of bipolar DC distribution network with multiple flexible equipment

The bipolar direct current distribution network (BDCDN) has the advantages of high reliability, large transmission, and high efficiency. However, voltage unbalance is a crucial power quality problem of BDCDN. On one hand, flexible equipment, such as DC electric spring, DC power flow controller, and DC transformer, can effectively suppress unbalanced voltage. On the other hand, the diversity of topology and control methods of multiple types of flexible equipment complicates power flow calculation. In this study, a linear power flow algorithm is proposed. First, the structural characteristics of a BDCDN with multiple types of flexible equipment are analyzed. Second, a linear ZIP load model based on Taylor expansion is derived. The steady-state model of multiple types of flexible equipment is established by analyzing the topological structure and control mode. Third, a network modeling and power flow calculation method of BDCDN with multiple types of flexible equipment are proposed. Finally, the modified IEEE14-node case and IEEE33-node case are used to verify the validity and correctness of the proposed algorithm. The effectiveness of flexible equipment on the power quality issue is demonstrated through comparison studies of power flow distributions.

Evaluation of a Passive-Based Controller for Power Monitoring in Networks of High Voltage Transmission Lines in Direct Current with Voltage Source Converters (VSC–HVDC)

In this paper a tracking Passivity--based Control (PBC) for a multiterminal Voltage Source Converter based High Voltage Direct Current Network (VSC--HVDC) is evaluated. First, the system (an actual multiterminal HVDC) described as a Port Hamiltonian (PH) System and the controller are presented and subsequently three scenarios are proposed to evaluate the closed--loop behavior, namely: (i) load changes; (ii) generation changes and, (iii) DC--bus changes. Numerical simulations are carried out and results shown the robustness of the closed--loop to cope with these common disturbances.

Empirical Filtering-Based Artificial Intelligence Learning Diagnosis of Series DC Arc Faults in Time Domains

Direct current (DC) networks play a pivotal role in the growing integration of renewable energy sources. However, the occurrence of DC arc faults can introduce disruptions and pose fire hazards within these networks. In order to ensure both safety and optimal functionality, it becomes imperative to comprehend the characteristics of DC arc faults and implement a dependable detection system. This paper introduces an innovative arc fault detection algorithm that leverages current filtering based on the empirical rule in conjunction with intelligent machine learning techniques. The core of this approach involves the sampling and subsequent filtration of current using the empirical rule. This filtering process effectively amplifies the distinctions between normal and arcing states, thereby enhancing the overall performance of the intelligent learning techniques integrated into the system. Furthermore, this proposed diagnosis scheme requires only the signal from the current sensor, which reduces the complexity of the diagnosis scheme. The results obtained from the detection process serve to affirm the effectiveness and reliability of the proposed DC arc fault diagnosis scheme.

A Robust Conic Programming Approximation to Design an EMS in Monopolar DC Networks with a High Penetration of PV Plants

This research addresses the problem regarding the efficient operation of photovoltaic (PV) plants in monopolar direct current (DC) distribution networks from a perspective of convex optimization. PV plant operation is formulated as a nonlinear programming (NLP) problem while considering two single-objective functions: the minimization of the expected daily energy losses and the reduction in the expected CO2 emissions at the terminals of conventional generation systems. The NLP model that represents the energy management system (EMS) design is transformed into a convex optimization problem via the second-order cone equivalent of the product between two positive variables. The main contribution of this research is that it considers the uncertain nature of solar generation and expected demand curves through robust convex optimization. Numerical results in the monopolar DC version of the IEEE 33-bus grid demonstrate the effectiveness and robustness of the proposed second-order cone programming model in defining an EMS for a monopolar DC distribution network. A comparative analysis with four different combinatorial optimizers is carried out, i.e., multiverse optimization (MVO), the salp swarm algorithm (SSA), the particle swarm optimizer (PSO), and the crow search algorithm (CSA). All this is achieved while including an iterative convex method (ICM). This analysis shows that the proposed robust model can find the global optimum for two single-objective functions. The daily energy losses are reduced by 44.0082% with respect to the benchmark case, while the CO2 emissions (kg) are reduced by 27.3771%. As for the inclusion of uncertainties, during daily operation, the energy losses increase by 22.8157%, 0.2023%, and 23.7893% with respect to the benchmark case when considering demand uncertainty, PV generation uncertainty, and both. Similarly, CO2 emissions increase by 11.1854%, 0.9102%, and 12.1198% with regard to the benchmark case. All simulations were carried out using the Mosek solver in the Yalmip tool of the MATLAB software.

Design of the Superconducting AC and DC Distribution for the ASCEND Demonstrator at Airbus

The ground-based Advanced Superconducting and Cryogenic Experimental power train Demonstrator (ASCEND) at Airbus intends to demonstrate the potential and feasibility of a cryogenic and superconducting powertrain as a breakthrough electric propulsion solution on future electric aircraft. A direct current distribution network is used in a propulsion chain to transfer 500 kW of power from the source to an electrical converter, which transforms the power into an alternating voltage/current to drive a superconducting motor. The working point of 1,700 A and 300 V is chosen for safety and installation reasons by operating at relatively low voltage. The direct current (DC) bus of ASCEND will be formed by a pair of high-temperature superconducting CORC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> cables inserted into a 10-meter-long narrow cryostat, resulting in a compact and lightweight solution. The 2-meter-long alternating current (AC) bus between the inverter and the electric motor is formed by a three-phase CORC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> cable. The challenge associated with 500 Hz operation in which a balance between AC loss in the cable and the size and mass of the system needs to be found, will be outlined. The AC and DC buses include several devices that connect the liquid nitrogen cooled power cables with the other system components that, in the case of the room temperature generator, operate at significantly higher temperatures. These devices thus include conduction-cooled current leads that are dimensioned to minimize the heat inleak from the warm to the cold environment. An overview of the design of the AC and DC buses and connecting devices will be provided and some of the design and operational challenges will be outlined.

Coordinated optimization model for solar PV systems integrated into DC distribution networks

AbstractSolar photovoltaic (PV) systems will drive deep electrification of energy systems leading to clean energy 2050. However, connecting large amounts of solar PV systems on direct current (DC) networks, like solar farms and potential future DC distribution systems, would lead to over voltages and loss of solar PV power output due to voltage issues. Further, current PV integration within distribution networks operate exclusively to maximize output using maximum power point tracking algorithms, without network coordination, which may lead to reduced solar output due to voltage issues. Here, a coordinated optimization model for solar PV systems and distribution network voltage regulators is presented. The proposed model optimally controls the settings of voltage controllers (DC‐DC converters), placed at the outputs of solar PV units and selected distribution lines, while maximizing solar power output and minimizing substation power (i.e. system losses). The solar PV systems are modelled using a trained neural network. Testing various systems against uncoordinated situations revealed that the proposed model yielded an increase in solar power of up to 60.06%, in the 28‐bus case. The proposed method will be an excellent tool enabling deep electrification using solar PV system and it overcomes limitations of uncoordinated systems used in practice today.

Compensation Method for Parallel and Iterative Real-Time Simulation of Electromagnetic Transients

Parallelization allows accelerating the computation of Electromagnetic Transients (EMTs). It can rely on the natural propagation delay of transmission lines (line-delay) to decouple a network into sub-networks without any loss of accuracy. Other techniques have to be used when there is no line-delay available. This paper presents one of them, using the Compensation Method (CM). This method is applied to decouple and parallelize real-time EMT simulations. The main novelty towards previous works is the introduction of an iterative version of CM to handle nonlinearities. The performance and accuracy of CM is studied through test cases, including practical distribution and High Voltage Direct Current (HVDC) networks. Hardware-In-the-Loop (HIL) setups with Line-Commutated Converters (LCC) and Voltage Source Converters (VSC) are used to test the iterative CM on practical real-time nonlinear cases.

Protection of radial MVDC electric network based on DC circuit breaker and DC fuses

The medium voltage direct current (MVDC) electric networks are emerging in power distribution and collection. The MVDC is an attractive solution in the applications involving DC loads or sources where high energy efficiency and high power flow controllability are required. The emergence of MVDC networks strongly relies on the availability of the appropriate protection strategies and equipment. This article proposes a protection strategy for a multi-terminal radial MVDC network based on the principle commonly used in the existing AC distribution networks. The protection strategy involves a single DC circuit breaker (DCCB) and multiple DC fuses. The proposed strategy limits the quantity of sophisticated and costly DCCB used. The cost-effective DC fuses are proposed to protect the parts of the network where the expected short-circuit occurrence is limited and where the automatic reclosing is not mandatory. The article concludes that low grounding resistance is beneficial allowing to easily isolate the faulty circuit. The simulation models are developed allowing to confirm the theoretical analysis.

Solving the Power Flow Problem in Bipolar DC Asymmetric Distribution Networks Using Broyden's Method.

This research addresses the power flow analysis in bipolar asymmetric direct current (DC) networks by applying Broyden's numerical method. This general successive approximations method allows for a simple Newton-based recursive formula to reach the roots of multiple nonlinear equations. The main advantage of Broyden's approach is its simple but efficient structure which can be applied to real complex nonlinear equations.The power flow problem in bipolar DC networks is still challenging, as multiple operating options must be considered, e.g., the possibility of having a solidly grounded or floating neutral wire. The main goal of this research is to contribute with a generalization of Broyden's method for the power flow solution in bipolar DC networks, with the main advantage that, under well-defined conditions, this is a numerical method equivalent to the matricial backward/forward power flow, which is equivalent to the successive approximations power flow method. Numerical results in the 21-, 33-, and 85-bus grids while considering two connections for the neutral wire (i.e., solidly grounded at any node or floating) show the effectiveness of Broyden's method in the power flow solution for bipolar asymmetric DC networks. All numerical simulations were carried out in the MATLAB programming environment.

MANA Formulation Based Load Flow Solution for DC Distribution Networks

This paper presents an efficient load-flow (LF) solution method for direct current distribution networks (DC-DNs). The principles of this method are based on the modified-augmented-nodal-analysis (MANA) formulation and Newton-Raphson (NR) algorithm. The guaranteed convergence and quadratic convergence conditions are also formulated using Kantorovich’s theorem. The modified IEEE 33 bus test feeder is simulated to test the proposed method and compare its performance with Laplacian Matrix based LF methods, Holomorphic Embedding LF method (HE-LFM) and classical Gauss-Seidel (GS) solution. Apart from the comparisons with these numerical methods the accuracy of the proposed method is also validated with Electromagnetic Transients (EMT) results. The proposed method offers much better convergence properties with a faster simulation speed.